Also having a knife go through Abby’s head, and the resulting explosion of gore, just maybe wouldn’t fit in with the general ‘tone’ of the comic.

Not really. MC included scenes of Anna beheading the Lord of Shadows, and we saw Dakota ambush Anna from behind by running her through with a sword.

Also, a knife through the skull would hardly result in a shower of gore. A stab wound can be quick and relatively clean (as in, little to no mess afterward). It'd also depend on the type of blade being used. A dart, or kunai (for example), may result in only a pinprick sized opening, but still be lethal enough to kill via poisoning, or internal bleeding.